Niacin and its derivatives are the most utilized coenzyme in the body, needed for over 400 different biochemical reactions. This article will discuss what niacin is, including its role in the body, how a niacin deficiency can occur, and how to ensure proper amounts of niacin in your diet.

What is Vitamin B3 (Niacin)?

Vitamin B3, commonly known as Niacin, is a water-soluble vitamin that all tissues in the body utilize. After being absorbed in the stomach and small intestine, niacin is converted into nicotinamide adenine dinucleotide (NAD). NAD is metabolically active on its own but, with the exception of skeletal muscle, has the potential to convert into nicotinamide adenine dinucleotide phosphate (NADP) in tissues.

While niacin is found naturally in foods, the amino acid tryptophan can also convert into niacin and is viewed as a source of niacin.

What is Vitamin B3's (Niacin's) Role in The Body?

As mentioned previously, niacin, in its cofactor forms of NAD and NADP, is required for over 400 reactions in the body. NAD is required to create energy from carbohydrates, proteins, and fats. NAD is also required for cellular functions, including gene expression, cellular communication, and maintenance of genes. NADP is required for the production of cholesterol (which in turn will make hormones, vitamin D, and cell membranes) and fatty acids. NADP is also necessary for antioxidant functioning; antioxidants neutralize free radicals, compounds that can disrupt cell functioning, including destroying DNA.

What Causes Vitamin B3 (Niacin) Deficiency?

Niacin deficiency is usually the result of a lack of dietary intake or problems with the conversion of tryptophan to niacin, which typically occurs due to other nutrient deficiencies.

People who are undernourished, including those with conditions such as inflammatory bowel disease (IBD), anorexia, AIDS, liver cirrhosis, and alcohol use disorder, are at an increased risk of niacin deficiency. Additionally, impoverished people are often undernourished and can lack proper niacin levels.

Low levels of riboflavin (vitamin B2), pyridoxine (vitamin B6), and iron are at an increased risk of niacin deficiency. These vitamins are required for the conversion of tryptophan to niacin; without them, tryptophan stays intact, resulting in less niacin. Concerning tryptophan, people with Hartnup disease, a genetic condition characterized by the lack of absorption of tryptophan, can result in low niacin levels. Lastly, people with carcinoid syndrome have lower levels of niacin. Carcinoid syndrome causes slow-growing tumors in the gastrointestinal tract and causes tryptophan to convert into serotonin, a neurotransmitter, rather than niacin.

Vitamin B3 (Niacin) Deficiency Symptoms

Severe niacin deficiency causes a condition called pellagra. Symptoms of pellagra include:

• Brown discoloration or rash on skin exposed to light
• Rough, sunburn skin appearance
• Bright red tongue
• Vomiting
• Constipation or diarrhea
• Depression
• Loss of interest/apathetic feelings
• Headaches
• Fatigue
• Loss of memory, potentially causing severe paranoia
• Suicidal ideations
• Hallucinations

If left untreated, pellagra can eventually lead to death.

How to Test Vitamin B3 Levels

Niacin levels can be measured in the blood and urine.

Blood levels of niacin can be measured, as offered by Access Medical Laboratories Vitamin B3 test. Reference ranges will vary depending on the specific lab.

Urinary levels of two breakdown products of niacin can be measured: N1-methyl-nicotinamide and N1-methyl-2-pyridone-5-carboxamide. Levels above 17.5 micromols/day suggest proper niacin levels. Levels between 5.8 and 17.5 micromols/day suggest low levels of niacin, and a level below 5.8 micromols/day would indicate a deficiency.

A niacin number and niacin index can also be measured. A niacin number indicates the ratio of NAD to NADP multiplied by 100. Levels below 130 represent a niacin deficiency. A niacin index is the ratio of red blood cells' NAD to NADP ratio; levels below one indicate a developing niacin deficiency.

Lastly, the DUTCH Complete test is a dried urine test that primarily evaluates sex and adrenal hormone metabolites. The DUTCH Complete also includes an organic acid test which has a marker, quinolinate, that, when high, can indicate a niacin deficiency.

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How to Get Enough Vitamin B3 from Your Diet

The FNB (Food and Nutrition Board) created Dietary Reference Intakes (DRIs) for various vitamins and minerals. One such DRI is the RDA (Recommended Dietary Allowance), defined as the average daily intake required to achieve nutritional adequacy in almost all healthy people. An Adequate Intake (AI) is formed when there is insufficient evidence to formulate an RDA. An AI is an amount of a vitamin or mineral assumed to reach nutritional adequacy.

RDA Niacin

RDA units of measurement of niacin are called niacin equivalents (NE)s. 1 NE is equivalent to 1 milligram (mg) of niacin or 60 mg of tryptophan.

Pregnant and lactating women have their own categories for DRIs as their nutrition needs differ from the general population of women. The RDA for pregnant women 14+ is 18 mg NE and for lactating women 14+ is 17 mg NE.

AIs are used as the DRI for birth to 1 year old. From birth to six months, the RDA for males and females is 2 mg of niacin only, as infants this age use all the protein, the source of tryptophan, they consume for growth and development. For seven months to 1 year, the RDA is 4 mg NE for males and females.

Food Sources of Niacin (B3)

Although niacin is found naturally in many foods, the United States and other countries have fortified the food supply with niacin.

B3 (Niacin) Supplements

Niacin is found in multivitamins, B complexes, and as a stand-alone supplement. Niacin in supplements is commonly found in the forms of nicotinic acid and nicotinamide. Additionally, inositol hexanicotinate is another form of niacin, although it usually results in about 30% less niacin absorbed than nicotinic acid or nicotinamide. Nicotinamide riboside and nicotinamide mononucleotide (NMN) are supplements derived from niacin, although they are not labeled as sources of niacin. It's important to note that in November 2022, the FDA ruled that NMN should not be labeled a supplement and "has been authorized for investigation by FDA as a new drug," according to the National Institutes of Health Office of Dietary Supplements.

How Much Niacin Is Too Much?

Niacin from dietary sources rarely results in high levels of niacin. However, niacin in supplement form can easily result in high levels. Niacin in supplements is commonly found in the forms of nicotinic acid and nicotinamide and will have different side effects. High doses of nicotinic acid, typically 30-50 mg or more, can lead to flushing of the face, arms, and chest with tingling, itching, and burning sensations. Accompanying symptoms include headaches, dizziness, and a drop in blood pressure may be found. This effect is generally not serious and will dissipate over time.

Recommendations to avoid these effects include taking niacin with meals or using a slow or delayed-release formula. Serious side effects of nicotinic acid are seen in doses of 1,000-3,000 mg/day. Doses in this range can cause blood pressure to drop enough to cause falls. Additionally, fatigue, blood sugar dysregulations, and gastrointestinal changes, including nausea, heartburn, pain, and vision changes, can occur. Chronic high-dose consumption can also lead to liver dysfunction, including liver failure; this is more common in extended-release nicotinic acid formulas.  

Nicatinominde does not cause flushing and adverse symptoms of nausea, vomiting, and liver toxicity are not seen until doses of 3,000mg/day or more are taken.

The FNB created Tolerable Upper Intake Levels (ULs) for niacin, defined as the maximum amount taken daily that is unlikely to cause adverse effects.

For pregnant and lactating women ages 14-18, the UL for niacin is 30mg; the UL for pregnant and lactating women ages 19+ is 35mg.

ULs have not been established for those under one year, as breastmilk, formula, and foods should be the only source of niacin in this age group.

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Summary

Niacin, or vitamin B3, is an essential vitamin involved in hundreds of processes throughout the body, including energy production, cholesterol creation, and antioxidant functioning. Because of its importance in the body, testing niacin levels can be insightful into how the body functions. Knowing levels can help assess a person's diet, ensuring that they receive enough dietary niacin. Supplementation is also an option, although one should take care when choosing the type and dose of niacin.